Solid state lighting (“SSL”) devices are designed to use light emitting diodes (“LEDs”), organic light emitting diodes (“OLEDs”), and/or polymer light emitting diodes (“PLEDs”) as sources of illumination, rather than electrical filaments, plasma, or gas. Solid-state devices, such as LEDs, convert electrical energy to light by applying a bias across oppositely doped materials to generate light from an intervening active region of semiconductor material. SSL devices are incorporated into a wide variety of products and applications including common consumer electronic devices. For example, mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize SSL devices for backlighting. Additionally, SSL devices are also used for traffic lighting, signage, indoor lighting, outdoor lighting, and other types of general illumination.
Microelectronic device manufactures are developing more sophisticated devices in smaller sizes while requiring higher light output with better performances. To meet current design criteria, LEDs are fabricated with decreasing footprints, slimmer profiles and are subsequently serially coupled in high voltage arrays. In certain embodiments, the individual SSL dies may include more than one LED junction coupled in series.
FIG. 1A is a cross-sectional view of a conventional high voltage SSL device 10a shown with two junctions in series in a lateral configuration. As shown in FIG. 1A, the high voltage SSL device 10a includes a substrate 20 carrying a plurality of LED structures 11 (identified individually as first and second LED structures 11a, 11b) that are electrically isolated from one another by an insulating material 12. Each LED structure 11a, 11b has an active region 14, e.g., containing gallium nitride/indium gallium nitride (GaN/InGaN) multiple quantum wells (“MQWs”), positioned between P-type GaN 15 and N-type GaN 16 doped materials. The high voltage SSL device 10a also includes a first contact 17 on the P-type GaN 15 and a second contact 19 on the N-type GaN 16 in a lateral configuration. The individual SSL structures 11a, 11b are separated by a notch 22 through which a portion of the N-type GaN 16 is exposed. An interconnect 24 electrically connects the two adjacent SSL structures 11a, 11b through the notch 22. In operation, electrical power is provided to the SSL device 10 via the contacts 17, 19, causing the active region 14 to emit light.
FIG. 1B is a cross-sectional view of another conventional LED device 10b in which the first and second contacts 17 and 19 are opposite each other, e.g., in a vertical rather than lateral configuration. During formation of the LED device 10b, a growth substrate (not shown), similar to the substrate 20 shown in FIG. 1A, initially carries an N-type GaN 15, an active region 14 and a P-type GaN 16. The first contact 17 is disposed on the P-type GaN 16, and a carrier 21 is attached to the first contact 17. The substrate is removed, allowing the second contact 19 to be disposed on the N-type GaN 15. The structure is then inverted to produce the orientation shown in FIG. 1B. In the LED device 10b, the first contact 17 typically includes a reflective and conductive material (e.g., silver or aluminum) to direct light toward the N-type GaN 15. A converter material 23 and an encapsulant 25 can then be positioned over one another on the LED structure 11. In operation, the LED structure 11 can emit a first emission (e.g., blue light) that stimulates the converter material 23 (e.g., phosphor) to emit a second emission (e.g., yellow light). The combination of the first and second emissions can generate a desired color of light (e.g., white light).
The vertical LED device 10b typically has higher efficiency than lateral LED device configurations. Higher efficiency can be the result of enhanced current spreading, light extraction and thermal properties, for example. However, despite improved thermal properties, the LED device 10b still produces a significant amount of heat that can cause delamination between various structures or regions and/or cause other damage to the packaged device. Additionally, as shown in FIG. 1B, the vertical LED device 10b requires access to both sides of the die to form electrical connections with the first and second contacts 17 and 19, and typically includes at least one wire bond coupled to the second contact 19, which can increase a device footprint and complexity of fabrication. Some of the conventional LED die processing steps have been restricted to the package level (e.g., after singulation at a die level (FIG. 1B)) to achieve high performance and prevent damage to the devices during processing steps. Such package-level processing steps increase demands on manufacturing resources such as time and costs as well as can have other undesirable results such as surface roughening of the package. Accordingly, there remains a need for vertical LEDs, vertical high voltage LED dies and other solid-state devices that facilitate packaging and have improved performance and reliability.